Makes me wonder if they are going to make it through the ruinstorm at all, that is sealing off the ultramar system. Considering that the Salamanders considers the Unbound Flame one of the lost treasures of Vulkan. His casket was labeled as the Unbound Flame in the Unremembered Empire.
Plus Vulkan did set in motion that only few of his treasures would be left, ordering the majority destroyed prior heading to Istvaan, fearing that they would end up in Horus' hands. But a loyal retainer persuaded him to spare some. vulkan naming him the guardian of them as the first forgefather.